This invention is directed to a method of producing oil from an oil-containing subterranean formation. More particularly, this invention is directed to a method of concentrating carboxylic acids that are present in crude oil and re-injecting the carboxylic acids into the oil-containing subterranean formation to enhance the efficiency of a caustic waterflood method of producing oil.
Waterflooding techniques have long been employed as secondary recovery techniques for recovering oil from subterranean oil-containing formations. Generally, in accordance with these techniques, at least an injection well and a production well are provided which communicate with the reservoir and water is injected via the injection well into the reservoir and oil is produced via the production well. Many modifications of the basic waterflooding techniques have been employed. These modifications include the use of various chemicals and materials in the water injected into the formation to improve the recovery of oil therefrom. Materials have been employed in the water to thicken the water and thereby improve the efficiency of the water for driving the oil from the formation. Surfactants have been included in the water to lower the interfacial tension between the oil and water in the formation and thereby facilitate their production therefrom. Such waterfloods are referred to as surfactant or low tension waterfloods. Caustic has been added to water to carry out what is referred to as a caustic waterflood. The injection of caustic into a formation brings about a reaction of the caustic with carboxylic acids present in the oil to form a surfactant in situ.
In an article by W. R. Foster entitled "A Low-Tension Waterflooding Process", published in the Journal of Petroleum Technology, February 1973, pp. 205-210, various aspects of displacement at low tension are discussed in general terms. In addition, there is discussed a low tension waterflooding process which consists of injecting three slugs of water with different chemical compositions, which slugs are denoted as a protective slug, a surfactant slug, and a mobility control slug. The protective slug is an aqueous solution of sodium chloride. The surfactant slug has the same sodium chloride content as the protective slug and contains sacrificial chemicals which may also be incorporated in the rear portion of the protective slug. The surfactant slug also contains a selected petroleum sulfonate. The mobility control slug has a sodium chloride content that is generally less than or equal to the other two slugs and contains a water-soluble biopolymer in a concentration sufficient to provide a locally stable mobility condition at the rear of the oil bank. The sequence of three slugs can be driven through the reservoir by the original reservoir brine.
Alkaline or caustic waters have been described for flooding certain types of reservoirs. For example, in U.S. Pat. No. 1,651,311 there is described a method for recovering oil from an oil-bearing formation by injecting a strong alkali, preferably in a saturated aqueous solution, into the formation. In U.S. Pat. No. 2,288,857, there is disclosed a technique for recovering petroleum from subsurface formations by injecting into the formation an aqueous solution which aids in stripping the petroleum from the formation and depressing the interfacial tension between the petroleum and the water and which effects emulsification of the petroleum. The emulsifying agent may be formed by a reaction between the components present in the petroleum and in the aqueous solution. Thus, when using aqueous solutions containing caustic alkali such as sodium and potassium hydroxides or ammonium hydroxide or alkali salts, an emulsifying soap may be formed by the reaction between the alkali and the organic acids naturally present in the petroleum. This type of emulsifying agent is useful mainly with restricted types of asphaltic crudes having sufficient acids of the proper molecular weight to yield an emulsifying agent on reaction with alkali.
In U.S. Pat. No. 3,927,716, there is described a process for the recovery of oil from a subterranean oil reservoir, which process involves the injection of an aqueous alkaline solution to neutralize organic acids in the reservoir oil to form surfactants in situ. The alkaline solution contains sufficient alkaline agent to impart a pH within the range of 11.5 to 13 and a monovalent salt within the range of 0.5 to 2.0 weight percent. The initial aqueous alkaline slug may be followed by a second alkaline slug containing a thickening agent. In U.S. Pat. No. 3,926,255, there is described a waterflooding process in which a petroleum oil containing divalent metal soaps is contacted with an inorganic acid in order to convert the soaps to the corresponding organic acids. The organic acids thus obtained may be injected into the reservoir followed by an aqueous alkaline solution Alternatively, the organic acids may be contacted with an aqueous alkaline solution in order to convert the acids to the corresponding surface-active monovalent salts which may be then injected into the reservoir.
In U.S. Pat. No. 3,929,190, there is described a process for the recovery of oil from a subterranean oil reservoir penetrated by spaced injection and production wells, which process involves the injection of an aqueous solution of neutralized organic acids extracted from a petroleum oil. An alkaline procedure is used for extracting the organic acids from the petroleum oil. The extract may be obtained at the oil field site or in conjunction with a refining operation. Subsequent to the injection of the aqueous extract of neutralized acids into the reservoir, a mobility-control slug may be injected in order to increase the sweep efficiency of the waterflood. In addition, a monovalent salt and an alkaline agent may be added to the aqueous extract solution prior to injection thereof.
In U.S. Pat. No. 3,823,776 there is described a technique for producing heavy oils having low acid values. By the technique there described, an oxygen-containing gas is injected into the formation to rapidly oxidize the oil and establish in the formation a stabilized in situ combustion zone. This results in the production of organic acids both in and surrounding the in situ combustion zone, thereby increasing the acid value of the oil. Thereafter, an aqueous, caustic solution is injected into the formation to quench the combustion in the in situ combustion zone and flow liquid aqueous caustic solution through the in situ combustion zone and into contact with the oil in the formation on the other side thereof and oil is produced from the formation.
In a paper entitled "Macroreticular Ion-Exchange Resins: Some Analytical Applications to Petroleum Products", by P. V. Webster, J. N. Wilson, and M. C. Franks, ANAL. CHIM. ACTA, 38 (1967) pp. 193-200, there is described the use of macroreticular strong ion-exchange resins for the separation from both model solutions and petroleum products of certain polar nonhydrocarbons. It is there pointed out that Munday and Eaves showed that orthodox ion-exchange resins can be used to absorb certain basic and nonbasic nitrogen compounds, alkylphenols and naphthenic acids from both model solutions and petroleum products. Their work was limited, however, by the fact that the ion-exchange resins they used were designed for use under aqueous conditions and were relatively inefficient in reacting with bulky organic molecules and nonaqueous media. Since their work was published, macroreticular ion-exchange resins designed for use in nonaqueous media have become commercially available. They differ from orthodox resins in possessing a spongelike structure with large pores of up to 1000 A (Angstrom) diameter, which are relatively unaffected by the solvent medium. Thus, large organic molecules in hydrocarbon solution may diffuse freely within the resin phase. In addition, the resin matrix possesses great mechanical strength and unlike orthodox resins shows no marked deterioration when subjected to repeated changes from an aqueous to a nonaqueous environment. The resins that were used in the work of Webster, Wilson, and Franks were Amberlyst 29, a quaternary ammonium anion exchanger, and Amberlyst 15, a sulphonic acid cation exchanger, both manufactured by Rohm and Haas; and Deacidite K, a macroporous anion-exchange resin manufactured by the Permutit Company Limited.